Check low battery indicator and change battery. Also check and adjust contact point of battery.

Not switching : Filter stays dark after the welding arc is extinguished or filter stays dark when no arc is present.

Check sensors and clean. Adjust sensitivity knob to the low position. If the welding place is extremely bright, it is recommended to reduce light level.

Switching or flickering : Filter darkens and then lightens while the welding arc is present

Check arc sensors are not blocked from direct access to the arc light. If the sensors are more than 120 degree the arc light, sensor may not work properly. Adjust sensitivity knob to the High position.

Side of the filter is brighter than the center of viewing area.

It is natural due to the character of LCD. This symptom is not harmful to the eyes. However for the maximum comfortable working condition, try to keep the viewing angle to the welding object close to 90 degree.